The present invention relates generally to seals for providing fluid sealing between a housing and a rotating shaft. More particularly, the invention relates to face seals in which a fluid is introduced between portions of the seal faces of the seal.
Conventional mechanical seals are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal between a rotating shaft and a stationary housing. The seal is usually positioned about the rotating shaft, which is mounted in and protrudes from the stationary housing. The seal is typically bolted to the housing at the shaft exit, thus preventing loss of pressurized process fluid from the housing. Conventional split mechanical seals include face type mechanical seals, which include a pair of annular sealing rings that are concentrically disposed about the shaft, and axially spaced from each other. The sealing rings each have sealing faces that are biased into physical contact with each other. Usually, one seal ring remains stationary, while the other ring contacts the shaft and rotates therewith. The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces into physical contact with each other. As a result of the repeated physical contact between the faces, abrasion of the seal faces occurs and the seals typically exhibit undesirable wear characteristics and leakage.
The poor wear characteristics of these conventional mechanical face seals necessitate the frequent monitoring and replacement of the seal components, particularly the seal rings. Replacement and repair of damaged seals have been facilitated by seal designs where a portion of the component parts of the mechanical seals are segmented or split. Installation of split or partially split seal components can be performed without necessitating the complete breakdown of the mechanical apparatus and without having to pass the annular seal over an end of the shaft. However, even in split seal designs, significant time is required to replace the seal components, resulting in frequent long periods of down time for the mechanical apparatuses associated with the seal.
The prior art attempted to overcome the above difficulties by employing non-contact mechanical seals that utilize a fluid interposed between the seal ring faces to reduce frictional wear. Conventional mechanical non-contact face seals typically employ spiral type-grooves formed in the hard face of the seal rings to develop a hydrodynamic lifting force that separates the seal faces. The resultant gap allows fluid to be disposed within the gap to prevent abrasion of the seal faces. These types of seals are limited in application because the seals are designed to operate in a unidirectional manner. If the seals are driven in the opposite direction, the seal rings typically do not separate but are pulled or sucked toward each other, thereby increasing wear and ultimately destroying the seals. Other conventional designs employ specially designed spiral grooves that can operate in both directions (bi-directional grooves). These grooves, however, are typically less efficient in separating the seal faces.
Even in mechanical non-contact seal designs a certain amount of seal face abrasion occurs, especially during start-up or during periods in which the shaft is rotating at relatively low speeds. Such abrasion causing wear of the seal components requires the eventual replacement of the seal components.
Few, if any, split-seal designs have been proposed for non-contacting seals. Difficulties have occurred in developing such a seal design due to the increased number of sealing surfaces in a split seal design and the presence of the fluid between the seal faces. The additional seal surfaces between each of the split segments of the seal components, and especially between the seal ring segments, make it difficult to maintain a fluid tight seal throughout the split seal. In addition, the fluid interposed between the seal faces can exert separation forces on the split seal components which can cause separation of the split components and further fluid leakage. For these reasons, there is a need in the art for a split, non-contact mechanical seal design that can provide a fluid-tight seal, while concomitantly providing the advantage of conventional split-seal designs.
As the above described and other prior art seals have proved less than optimal, an object of the present invention is to provide an improved split mechanical seal in which a fluid can be introduced between the seal faces while maintaining a relatively fluid-tight seal.
Another object of the invention is to provide a split mechanical seal operable under a wide range of operating conditions for a wide range of services.
Still another object of the present invention is to provide a split mechanical seal that is relatively easy to assemble or and to disassemble.
Yet another object of the invention is to provide a split mechanical seal that employs fluid at the seal faces to reduce wear while concomitantly preventing or minimizing leakage at the other faces, without compromising seal performance or integrity.
Other general and more specific objects of this invention will in part be obvious and will in part be evident from the drawings and the description which follow.